Storm Troopers (not those kinds of storm troopers), if being used 'formally,' are a very specific kind of soldiers found in the German Army in the latter half of World War One. Stosstruppen, as they are called in German were specialized detachments of soldiers who were used in the first waves of a German attack. Unlike many of their compatriots, storm troopers were equipped with a number of different kinds of weapons, including rifles, grenades, pistols, flame throwers, and eventually even primitive sub-machine guns. These soldiers trained constantly for their attacks, and prided themselves on their high operational tempo (they moved fast and hit hard). They would lead the German attacks, sneaking up to the Allied trenches during preliminary bombardments. Once the bombardment lifted, the storm troopers would jump into the trench and secure it while the Allied soldiers were still leaving their dugouts and manning their positions. Using their specialized training and weapons, the storm troopers were effective at penetrating defense, clearing trenches and dugouts, and paving the way for follow-up forces to fully secure the whole trench network. Ernst Junger, a German soldier, wrote a famous memoir Storm of Steel which describes his time as a Storm Trooper.

Grenadiers are a much older kind of soldier. They have their roots in the 17th and 18th century as specialized soldiers. Grenadiers got their name from the weapon which made them unique, the hand grenade. But at this time, grenades were a bit more primitive that what were used to. They consisted largely of an iron sphere, hollow on the inside, filled with black powder. The charge was detonated with a simple chord fuse, which caused the shell to fragment. However, these grenades were cumbersome in battle. Their fuses were unreliable, especially in damp weather, and required the thrower to be dangerously close to their enemy. The grenade was initially used as the precursor to a physical charge, as their users couldnt often be expected to throw them much further. And keep in mind the disastrous effect a short throw might have! To maximize their range and effectiveness, European armies formed grenadier companies in their most elite regiments. These companies, armed with both muskets and grenades, were the tallest, broadest, bravest soldiers in the regiment, and they had to be given their dangerous payloads. And to mark their special purpose, many of these units wore distinctive uniforms and special headgear. The most famous example of this are the tall hats, especially those of Napoleon's Grenadier Guard. However, there was an unplanned outgrowth as a result of forming these specialized companies. They quickly gained the reputation of being filled with the biggest, meanest, toughest members of the army, and when combined into their own regiments, these forces became the elite of most armies. Into the 19th century, Grenadier regiments had the reputation of being the soldiers you could most count on to get the job done, even after their iconic weapon had long been phased out! Grenadiers, in the literal sense, made a comeback in the 20th century as grenades became a more efficient and effective weapon. The modern US Army and Marine Corps utilize grenadiers, soldiers equipped with the dedicated M203 under barrel grenade launcher. However, these soldiers have lost a lot of the prestige once associated with their position. The reduced size of grenades means that now any soldier can effectively use them. But on an even deeper level, the term 'grenadier' no longer carries the same connotation of 'elite.' During the World Wars, many units in the European armies, and especially the Germans, had the title 'Grenadier' applied to them. This widespread use served to dilute a term which had already been slowly falling out of favor.

As for 'shock troopers,' unlike the other two terms, this is more of a colloquial term. It, and the other two used informally and less technically, refer to soldiers whose job is take ground. They are the soldiers who get in close, muscle the enemy off a position, and hold it for themselves. This, generally, is what military theorists call 'shock.' It includes many of the concepts weve already discussed, including overwhelming firepower, rapid tempo operations, physical prowess, and, of course, deadly effect. As a more general thing, this term can be applied to all kinds of different soldiers, it isnt limited to just one formation or group (though, the Red Army did employ 'Shock' Armies in the latter half of World War Two). Its less specific than 'storm trooper,' or 'grenadier,' which makes it popular in the public lexicon.